1. Field of the Invention
The present invention relates generally to a method and apparatus for downhole safety valve remediation using controlled detonation of a measured explosive charge.
2. Description of the Related Art
Subsurface safety valves are commonly used in wells to prevent uncontrolled fluid flow through the well in the event of an emergency, such as to prevent a well blowout. Conventional safety valves use a flapper, which is biased by a spring to a normally closed position, but is retained in an open position by the application of hydraulic fluid operating on a rod piston connected to the flapper valve from the earth's surface. A typical surface controlled subsurface safety valve ("SCSSV") is shown and described in U.S. Pat. No. 4,161,219, which is commonly assigned hereto.
Through normal operation of a well, scale and other debris can build up on the inner surface of the well tubing. In addition to the well tubing surface build-up, however, scale, asphaltines, and other debris can also build up within the bore of the safety valve as well as on the mechanical parts of the safety valve, themselves, to render the safety valve either more difficult to operate or even totally inoperative. Various methods and apparatus have been employed to remediate safety valves after such a scale or debris build-up. For example, coiled tubing has been used in connection with an orifice nozzle to remove the scale or debris build-up with fluid pressure. Further, a running tool may be used to remediate the valve. The running tool may have a tool profile adapted to mate with a well profile associated with the desired valve. When the tool reaches the desired location within the well, the tool may then be engaged within the well profile and mechanical force is applied to the tool, jerking the tool back and forth in hopes of freeing the valve from the binding force of the scale or other debris build-up. As an additional example, in the event the valve is stuck in the closed, or sealing, position a simple rod may be lowered into the well to the desired location within the safety valve and mechanical force is applied to mechanically beat downward on the flapper or other sealing member within the valve body in hopes that the mechanical force will overcome the binding force of the scale or other debris build-up within the valve.
There are other safety valve failures or problems that may arise that require safety valve remediation in a typical well operation. For example, a typical safety valve, as described above, may be maintained in its open position by maintaining hydraulic pressure through a hydraulic control line within the well casing extending from the safety valve to a source of hydraulic pressure at the well surface. In the event of, for example, a hydraulic pressure leak in the hydraulic control line or a hydraulic pump failure, hydraulic pressure may not be maintained to the safety valve. In such a situation, it may not be possible to maintain the safety valve in its fully open position in which case production fluid may be partially or completely restricted through the safety valve. It may not be possible or desirable to remove the safety valve in such a situation; therefore, various methods and apparatus have been employed to remediate safety valves in such a situation. Typically, a wireline inset valve may be inserted into the safety valve to lock out the valve to maintain the valve in its open position and permit production fluid to continue to flow through the valve. However, such methods and apparatus may be expensive and may not be desirable in a particular application.
Explosive charges have been employed in certain well operations, particularly in certain downhole electric line well operations. Previously, explosive charges have been used, for example, to: perforate well casing and any surrounding formation to permit fluid flow into the well casing from the formation; set and release packers for sealing off between the well casing and production tubing extending through the casing; and break up scale or other debris build-up from, for example, threaded tools or tubing joints to facilitate removing the tools or tubing string from the well. However, explosive forces have not heretofore been incorporated in a method or apparatus for remediation of downhole safety valves. In the case of scale and other debris build-up removal, it has not heretofore been possible or practical to effectively control the explosive forces within the safety valve body to remove the scale or other debris build-up while preventing undesirable destruction or damage to the safety valve or to lockout a defective safety valve while preventing or minimizing damage to proximate tubing or other apparatus within the well.
The prior methods and apparatus have not previously provided an adequate remediation solution for safety valves. Accordingly, there has developed a need to provide a method and apparatus for downhole safety valve remediation using precisely controlled explosive forces to remove scale and other debris build-up or to lockout a defective safety valve. The present invention has been contemplated to meet this need.